It is well known that surfaces of metallic workpieces that are subject to high levels of tribological stress such as the piston running surfaces of cylinder sleeves or cylinder bores in cylinder crankcases are mechanically roughened in order to obtain a good adhesive basis for a surface coating, in particularly applied by means of thermal spraying.
For example, WO 2010/015229 A1 proposes machining a cylindrical surface of an aluminium cast part using a follow-on tool by successively machining a groove cross-section to its final dimensions by means of consecutively engaging machining teeth. The tool specified for this purpose is configured as a follow-on tool comprising a first tooth referred to as a drill-out tooth to drill out the cylindrical surface to a predefined nominal diameter, several cutting teeth following the drill-out tooth to create and machine a groove and a non-cutting shaping tooth referred to as a displacement tooth. The cutting teeth, which are arranged in a comb-like series with a division which corresponds to the pitch of the helically extending groove to be created, comprise among other things several pre-machining teeth for the creation and successive machining of a base groove and several trapezoidal teeth following the pre-machining teeth for the successive further machining of the base groove to a trapezoidally undercut final cross-section. The trapezoidal teeth, which are asymmetrical in their cross-section shape, successively widen a base groove previously created by the pre-machining teeth in such a way that they undercut the base groove initially on one flank and then on the other flank so as to obtain a trapezoidally undercut final cross-section as required. The trapezoidally undercut final cross-section guarantees a mechanical grouting between a coating applied to the cylinder surface by means of thermal spraying and the aluminium cast part which exhibits the cylindrical surface. The aim of the successive, one-sided groove flank machining by means of trapezoidal teeth which are asymmetrical in their cross-section shape is to ensure that so-called smearing does not occur on the tool, because this causes shaping imprecisions in the desired groove structure when relatively soft materials are machined such as aluminium.
DE 10 2014 119 514 A1 criticises that in the grooves created as described above, the edges extending on the surface side are relatively thin in configuration so that cracks can form in the applied coating at these points as a result, and also that due to the tool geometries determined by the edges, at least sections of the teeth can break away. In order to avoid these problems, DE 10 2014 119 514 A1 proposes a method by which a machining tool comprising several cutting teeth with cross-sections of differing symmetries is initially used to create a helically extending base groove in a cylindrical surface of a workpiece, this base groove then being successively machined to create a trapezoidally undercut cross-section. Specifically, the proposal is to use at least a first cutting tooth to create the base groove with boundary surfaces running at a slant in relation to normals extending from the surface so as to form a first symmetrical, provisional groove geometry of a depth which is less than the groove in its final groove geometry; to use at least a second cutting tooth to machine the base groove in extension of the boundary surfaces up to or approximately up to the bottom of the groove in its final groove geometry so as to create a second provisional groove geometry; to create chamfers on the groove in its final groove geometry with at least a third cutting tooth by removing sections to create a third provisional groove geometry at the same time, these sections each extending from the bottom of the groove and from a straight line drawn through the bottom of the groove and a normal intersecting the boundary surfaces at one point in each case, by which the desired length of the chamfer is determined; and with at least a fourth cutting tooth at the same time to create the bottom of the groove and the flanks of the undercuts of the groove in its final groove geometry.
The method proposed in DE 10 2014 119 514 A1 is conceived in the same way as the method or tool for machining a cylindrical surface, in particular of an aluminium cast part, as proposed in WO 2010/015229 A1. However, processing other materials is not addressed in the above documents. Cylinder sleeves and cylinder crankcases are frequently made of other cast iron materials such as grey cast iron. Cast iron, e.g. grey cast iron, differs from aluminium in terms of its machinability and chip formation. For example, when machining cast iron such as grey iron, tearing chips (discontinuous chips) are formed which are torn out of the workpiece. Due to this tearing out of the chips, the surface of the workpiece has an undefined roughness. However, the tools and methods developed for machining aluminium cast parts as specified in the documents discussed above are only suitable to a limited extent or not at all for machining cast iron materials. On the contrary, special cutting profiles are required for machining cast iron, for example grey cast iron.